1. Field of the Invention
The present invention relates to lens actuators mainly used for cameras and mobile phones.
2. Background Art
In recent years, an increasing number of cameras and mobile phones have come to use a lens actuator to auto focus the lens and to correct blurring. In line with this, there is a growing demand for easy-to-use and reliable lens actuators.
A conventional lens actuator will be described with reference to FIGS. 9 to 12. FIGS. 9 and 10 are a sectional view and an exploded perspective view, respectively, of the lens actuator. FIGS. 11 and 12 are partial perspective views of this lens actuator. As shown in FIG. 9, the lens actuator includes carrier 1, driving coil 2 (hereinafter, coil 2), driving yoke 3 (hereinafter, yoke 3), driving magnets 4 (hereinafter, magnets 4), spacer 5, upper spring 6, lower spring 7, and case 8.
Carrier 1 is made of an insulating resin, is substantially cylindrical, and is vertically movably housed in yoke 3. Coil 2 is made of a copper alloy of a substantially ring shape, and is wound around the outer periphery of carrier 1 and fixed thereto. Yoke 3 is made, for example, of iron, and is shaped like a box having a circular center hole. Magnets 4 are substantially arc-shaped, and are arranged facing each other on the inner wall of yoke 3 with a predetermined space from coil 2. Spacer 5 is made of an insulating resin, and covers the bottom surface of the outer periphery of yoke 3.
Upper and lower springs 6 and 7 are sheet metals. Case 8 is made of an insulating resin. Upper spring 6 is fixed in a slightly bent state to the top surface of yoke 3, and lower spring 7 is fixed to the top surface of case 8. Upper and lower springs 6 and 7 are in elastic contact with the top surface and the bottom surface, respectively, of carrier 1 so as to hold carrier 1 in position in the vertical direction, thereby forming drive unit 10 shown in FIG. 10.
The lens actuator further includes base 11, slider 12, support pins 13A and 13B, moving coils 14 (hereinafter, coils 14), moving magnets 15 (hereinafter, magnets 15), and cover 16.
Base 11 and slider 12 are made of an insulating resin. Slider 12 has support holes 12A into which columnar support pin 13A is inserted. Base 11 has holding members 11A into which both ends of support pin 13A are locked. As a result, slider 12 is mounted on base 11 movably in the back-and-forth direction.
Case 8 has support holes (not shown) into which support pin 13B is inserted. Slider 12 has holding members 12B into which both ends of support pin 13B are locked. As a result, drive unit 10 is mounted on slider 12 movably in the right-and-left direction.
Thus, drive unit 10 is movable with respect to base 11 via slider 12 both in the back-and-forth direction and in the right-and-left direction.
Coils 14 are made of a copper alloy wound in the shape of frames, and are fixed to the four side surfaces of yoke 3 of drive unit 10. Magnets 15 are substantially rectangular, and are arranged facing each other on the inner wall of cover 16 with a predetermined space from coils 14. Cover 16 is made of a metal, and is shaped like a box having a circular center hole.
As shown in FIG. 11, magnets 15 each have N and S poles arranged in the back-and-forth or right-and-left direction. Coils 14 facing magnets 15 each have an inward magnetic field B1, which is orthogonal to the vertical direction.
Base 11, slider 12, coils 14 (14A, 14B, 14C, 14D), and magnets 15 together form move part 18 shown in FIG. 12. Cover 16 covers move part 18 and drive unit 10.
The above-structured lens actuator with a lens (not shown) in the hollow of carrier 1 and an image pickup device behind the lens is attached to an electronic device such as a camera or a mobile phone. Driving coil 2 and moving coils 14 are connected to an electronic circuit (not shown) of the electronic device via lead wires or connectors (not shown).
In this electronic device, when the user lightly presses, for example, a push button (not shown) of camera, the electronic circuit applies voltage to coil 2 so as to supply current thereto. Magnets 4 and yoke 3 together form a magnetic field around magnets 4 directed inward or outward. As a result, coil 2 is subjected to a force in the vertical direction, which is orthogonal to the magnetic field. This allows carrier 1 including coil 2 wound therearound and fixed thereto to move in the vertical direction, allowing the auto focus to adjust the focal position of the lens in the hollow of carrier 1.
When the current supply to coil 2 is interrupted, carrier 1 is pressed by the biasing force of upper and lower springs 6 and 7 which are in elastic contact with the top surface and the bottom surface, respectively, of carrier 1. As a result, carrier 1 returns to the original position.
When the user strongly presses the push button of camera, causing blurring, the blurring is detected by the electronic circuit of the electronic device through, for example, a separate sensor (not shown). Then, the electronic circuit applies voltage to coils 14 so as to supply current thereto. As a result, coils 14 are subjected to a force in the back-and-forth or right-and-left direction. This allows yoke 3 of drive unit 10 including coils 14 fixed thereto to move in the back-and-forth or right-and-left direction, thereby correcting blurring.
When coils 14 having an inward magnetic field B1 around them are supplied with a clockwise current I1 as shown in FIG. 11, coils 14 are subjected to a forward force F1, thus moving drive unit 10 in the forward direction. When supplied with a counterclockwise current 12, on the other hand, coils 14 are subjected to a backward force F2, thus moving drive unit 10 in the backward direction.
Thus, in FIG. 12, drive unit 10 on slider 12 moves in the back-and-forth direction when current is supplied to moving coil 14A or 14B, and moves in the right-and-left direction when current is supplied to moving coil 14C or 14D.
In short, the auto focusing is performed by supplying current to coil 2 facing magnets 4 so as to vertically move carrier 1, thereby vertically moving the lens in the hollow of carrier 1. The shaking correction (optical image stabilization) is performed by supplying current to coils 14 facing magnets 15, thereby moving yoke 3 of drive unit 10 in the back-and-forth or right-and-left direction.
An example of a conventional technique related to the present invention is shown in Patent Literature 1.
In this conventional lens actuator, magnets 15 arranged outside carrier 1 have the magnetic field B1, which is directed toward the inside of carrier 1, that is, toward yoke 3 including coil 2 and magnets 4. Therefore, when having a strong magnetic force, magnets 15 affect coil 2 and magnets 4, possibly preventing carrier 1 from moving precisely in the vertical direction.
Citation List
Patent Literature 1: Japanese Patent Unexamined Publication No. 2008-32768